This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-177307, filed Jun. 13, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a circuit pattern design method, exposure method, and charged-particle beam exposure system for a character projection type charged-particle exposure technique.
Electron beam exposure is an effective means for processing the micropattern of a semiconductor circuit. A VSB (Variable Shaped Beam) exposure method as a typical electron beam exposure method divides a circuit pattern into small rectangles or triangles and repetitively exposes them, which increases the number of electron beam shots and decreases the throughput. To prevent this, a CP (Character Projection) exposure method of shaping an electron beam into the shape of a figure with a size of several micro meter square and exposing a figure (character) at once is adopted to decrease the number of shots and increase the throughput. The electron beam is shaped via a CP aperture mask having character-shaped apertures.
The CP exposure method with electron beam extracts figures to be exposed by CP exposure method from a circuit pattern to be exposed, and performs exposure by using a CP aperture mask formed from a set of beam shaping characters corresponding to the figures.
FIG. 5 shows the schematic arrangement of an electron beam exposure apparatus. As shown in FIG. 5, an electron beam 602 emitted by an electron gun 601 is shaped into a beam with square cross section by a first shaping aperture 603. The shaped electron beam 602 irradiates via a character selection deflector 604 a character which is a transmission window formed in a CP aperture mask 605. The electron beam 602 having passed through the transmission window of the character is reduced by a reduction lens 606 and irradiates a desired position on a sample 608 via an objective deflector 607.
The arrangement of the CP aperture mask 605 shown in FIG. 5 will be described with reference to FIG. 6. As shown in FIG. 6, a plurality of aperture blocks 701 corresponding to respective deflection regions of the character selection deflector 604 are laid out on the CP aperture mask 605. A character-shaped transmission window 702 laid out within each aperture block 701 can be freely selected in exposure.
If the character shape formed in the aperture block is not a pattern frequently used in a semiconductor circuit pattern to be exposed, the effect of reducing the number of electron beam shots is poor. In other words, an aperture block formed from a character optimal for electron beam exposure must be prepared for each semiconductor circuit pattern (semiconductor device). One aperture block must be selected in exposure in correspondence with one semiconductor circuit pattern to be exposed.
A conventional pattern data design method is shown in the flow chart of FIG. 7. The designer designs circuit patterns (step S301). Repetitively used figures are extracted from the designed device patterns and set as characters to be exposed by CP exposure method (step S302).
A CP aperture mask having the extracted character shapes is prepared (step S303), and set in an electron beam exposure apparatus. The positions of CP apertures are selected to allow the character selection deflector to select an aperture block to be used (step S304). The circuit patterns are classified into characters to be exposed by CP exposure method and figures to be exposed by VSB exposure method, and they are converted into exposure data corresponding to the exposure apparatus (step S305).
The converted data are input to the exposure apparatus, and a sample such as a resist film on a silicon wafer or mask substrate is exposed with an electron beam by using a selected aperture block (step S306).
Conventionally, the operator who executes exposure selects and sets a corresponding aperture mask, or selects an aperture block to perform exposure. For example, Japanese Patent No. 2,885,778 discloses a method of setting an index to a circuit pattern or aperture mask and determining whether the index of the aperture mask set in the exposure apparatus is appropriate for a pattern to be exposed.
This method forms an aperture mask every time a circuit pattern is formed, which makes management of the circuit pattern and aperture mask difficult. If human errors in setting an aperture mask increase, or circuit patterns and CP apertures used for exposure increase, it becomes difficult to associate the circuit patterns with CP aperture and a desired pattern cannot be easily exposed.
(1) There is provided a circuit pattern design method for generating a circuit pattern from a logic description which describes circuit operation of a semiconductor device in a charged-particle beam exposure system having a charged-particle beam exposure apparatus for forming a pattern on a sample by charged-particle beam exposure using both a character projection exposure method and a variable shaped beam exposure method, a standard cell library which stores standard cells that optimize circuit patterns for function units, and a CP aperture mask management table which stores an index unique to each aperture block that is formed on an aperture mask used for exposure by the character projection exposure method and bears characters corresponding to the standard cells, information of the standard cells corresponding to the characters laid out on each aperture block, and the number of charged-particle beam shots necessary to expose all the characters corresponding to the standard cells by the character projection exposure method, comprising the step of generating a circuit pattern from the logic description for each aperture block by using standard cells corresponding to characters formed in one aperture block, and associating each circuit pattern with an aperture block used to generate the circuit pattern, the step of extracting a circuit pattern which satisfies a predetermined constraint condition from a plurality of generated circuit patterns, and the step of selecting a circuit pattern that requires a smallest number of charged-particle beam irradiation operations when charged-particle beam exposure is performed by using an aperture block corresponding to the extracted circuit pattern.
(2) According to the present invention, there is provided an exposure method comprising the steps of converting a circuit pattern designed by using the above-described circuit pattern design method into exposure data to be input to an exposure apparatus, selecting an aperture mask bearing an aperture block corresponding to the exposure data by looking up a CP aperture mask management table for the aperture block corresponding to the input exposure data, setting the aperture mask in a charged-particle beam exposure apparatus to move the aperture block used in a charged-particle beam irradiation enable range, and transferring a predetermined pattern onto a sample by using the aperture block.
(3) According to the present invention, there is provided a charged-particle beam exposure system comprising a charged-particle beam exposure apparatus for forming a pattern on a sample by charged-particle beam exposure using both a character projection exposure method and a variable shaped beam exposure method, a standard cell library which stores information of a plurality of standard cells that optimize circuit patterns for function units, an aperture mask which is set in the charged-particle beam exposure apparatus, bears characters corresponding to the standard cells, and has an aperture block falling within an irradiation range of the charged-particle beam exposure apparatus, a CP aperture mask management table which stores an index unique to each aperture block that is formed on the aperture mask and bears the characters corresponding to the standard cells, information of the standard cells corresponding to the characters laid out on each aperture block, and the number of charged-particle beam shots necessary to expose each character corresponding to the standard cell by the character projection exposure method, and a design unit for designing a layout by looking up the standard cell library and the CP aperture mask management table.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.